This invention relates to a tandem rolling mill train for metal plate and sheet, and more particularly to a tandem rolling mill train including a cross-roll type rolling mill stand.
The flatness or the cross-sectional shape of rolled plate or sheet (hereinafter called the strip) of steel and the like is sometimes impaired by the uneven elongation across its width.
One technique for controlling the widthwise thickness distribution during rolling employs rolling rolls curved by applying hydraulic force on the roll chocks thereof so that the profile of the roll gap through which the piece passes is varied. This technique is known as the roll bending method.
But this method can control the widthwise thickness distribution only to a limited extent since the bending of work rolls is restricted by backup rolls etc.
The technique disclosed in Japanese Patent Publication No. 19821 of 1977 and Japanese Patent Laid Open No. 64908 of 1980 offers a solution to this problem. This method may be termed crossed-roll rolling. It controls the thickness distribution across the width of the strip being rolled by changing the angle formed between the axis of the crossed work rolls and the direction of strip travel, within a plane parallel to the surface of the piece. A rolling mill based on this crossed-roll concept is disclosed, for example, in Japanese Patent Publication No. 1221 of 1978.
The top and bottom work rolls based on the cross-roll concept lie diagonally across the width of a strip 1. Because of this roll arrangement, as shown in FIG. 1, oppositely oriented shearing forces F work on the top and bottom surfaces of the strip 1 across the width thereof, so that the cross-sectional shape across the width of the strip 1, which is rectangular at the start, becomes parallelogramic after being rolled.
When the corners of the cross section of the strip 1 considerably deviate from 90 degrees, the edge 3 of an acute-angled corner 2 (.alpha.&lt;90.degree.) must be trimmed off since such portion might get bent, thus becoming unsuited for shipment, during handling. Such trimming naturally lowers the production yield of strip. If a parallelogramic strip is passed through a subsequent processing line, the edge 3 of the acute-angled corner 2 might get damaged upon coming in contact with the guide of the line, possibly causing the breaking of the strip.
Thus, rolling on a crossed-roll mill involves various operational problems.